Trail Design

The AASHTO Guide for the Development of Bicycle Facilities (1999) and Trails for the 21st Century have extensive information on how to design trails. Some states also have their own design manuals that match or exceed these guidelines. Some of the most critical design considerations include the following:

Trails should be at least 10 feet (12 feet is often preferred) with two feet of clear space on both sides of the trail.
Assume pedestrians and bicyclists will use the trail — design for both.
Most urban trails have an asphalt surface which accommodates more user types (e.g. roller bladders); many rural trails have crushed limestone, which is cheaper but may require more maintenance.
The AASHTO guide provides detailed information on horizontal alignment, curve radii, grade, structures, and other design elements affecting trail alignment.
Give special attention to intersections since they are where crashes between trail users and motorists are most likely to occur. In addition to following AASHTO, follow the Manual on Uniform Traffic Control Devices (MUTCD) to determine the type of traffic control device to use.
Roadway Separation:
Sidewalk trails immediately adjacent to roadways are generally discouraged. However, they can be made safe if they are separated from the roadway by at least five feet or a 42 inch high barrier. Again, AASHTO provides excellent guidance on when and where this type of facility is appropriate.